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ABSTRACT: Understanding of the basic nature of arc root fluctuation is still one of the unsolved problems in thermal arc plasma physics.
It has direct impact on myriads of thermal plasma applications being implemented at present. Recently, chaotic nature of arc
root behavior has been reported through the analysis of voltages, acoustic and optical signals which are generated from a
hollow copper electrode arc plasma torch. In this paper we present details of computations involved in the estimation process
of various dynamic properties and show how they reflect chaotic behavior of arc root in the system.
Pramana 04/2012; 59(1):143-150. · 0.57 Impact Factor
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ABSTRACT: The characteristics of metal plasma launched by high-current electric arc in a vacuum-arc rail gun are determined by employing electrical and magnetic probes. These measurements are validated by results from theoretical simulations. The arc coupled nonlinear circuit equations are solved simultaneously with the Newtonian arc motion and revealed the undercritically damped behavior of the arc current identical to the arc-current signal recorded by the Rogowski magnetic probe. Similarly the arc velocity and displacement derived from the signatures of B -dot probes are shown to concur closely with the results of J×B propulsion from simulation. The heating of plasma is formulated in a three-electron population regime with direct arc energy coupling through magnetohydrodynamic, ion-acoustic, Coulomb, and neutral interactions. This results in high temperature (T<sub>e</sub>) of hundreds of eV in the arc as revealed by the simulation. Hence T<sub>e</sub> of the rapidly cooling and equilibrating plasma that emerged from the muzzle is high around 80–90 eV , which is confirmed by Langmuir electric probe measurements. Density n<sub>e</sub> of this metal plasma is shown to be in the range 4×10<sup>21</sup>–6×10<sup>21</sup> m <sup>-3</sup> and includes multiple ion charge states. The exit velocity of the plasma measured by a pair of Langmuir probes is close to 2.2×10<sup>6</sup> cm / s and matched well with the arc velocity determined by the B -dot probes and the results from simulation.
Journal of Applied Physics 11/2004; · 2.17 Impact Factor
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ABSTRACT: Arc coupled nonlinear LCR circuit equations were solved simultaneously with the Newtonian arc motion to describe the under-critically damped high arc current and resulting _J × _B propulsion in a vacuum-arc rail gun. Heating of plasma owing to the direct coupling by arc through magneto-hydrodynamic, ion-acoustic, Coulomb, and neutral interactions is formulated in a three-component electron continuity regime including major loss by radiation. The plasma density (n<sub>e</sub>) so deduced in arc was around 10<sup>22</sup>-10<sup>23</sup>m<sup>-3</sup>, temperature (T<sub>e</sub>) over hundreds of electronvolts, and attained final velocity ∼2×10<sup>6</sup>cm/s. The launched plasma on emerging from the gun muzzle, rapidly equilibrated through radiative re-combinations and three-body collisions has n<sub>e</sub>∼5×10<sup>21</sup>m<sup>-3</sup> and T<sub>e</sub>∼80-90 eV at 50 cm away from the breech as shown through experiments.
IEEE Transactions on Plasma Science 05/2004; · 1.17 Impact Factor
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ABSTRACT: The electron number density has been measured in a plasma spray torch using Stark broadening of H
b_{\beta}
and Ar-I (430 nm) line. A small amount of hydrogen (1% by volume in argon gas) was introduced to study the H
b_{\beta}
line profile. Axial variation of electron number density has been determined up to a distance of 20 mm from the nozzle exit point of spray torch. The plasma torch was operated at 5 and 10 kW power level and flow of argon was kept at 25 liters per minute. Using the measured excitation temperature data under same experimental conditions, the electron number density has also been calculated using Saha equation. Comparison of electron number densities measured from Stark broadening with those derived from excitation temperature measurements under the assumption of local thermodynamic equilibrium (LTE) in thermal plasma jets indicate about the deviation from LTE in thermal plasma jets. The electron number density measurement using Stark broadening of Ar-I (430 nm) line will be particularly useful when only argon gas is used in thermal plasma jets.
The European Physical Journal D 01/2003; 26(2):215-219. · 1.48 Impact Factor
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ABSTRACT: The electron number density has been measured in a plasma spray torch using Stark broadening of H β and Ar-I (430 nm) line. A small amount of hydrogen (1% by volume in argon gas) was introduced to study the H β line profile. Axial variation of electron number density has been determined up to a distance of 20 mm from the nozzle exit point of spray torch. The plasma torch was operated at 5 and 10 kW power level and flow of argon was kept at 25 liters per minute. Using the measured excitation temperature data under same experimental conditions, the electron number density has also been calculated using Saha equation. Comparison of electron number densities measured from Stark broadening with those derived from excitation temperature measurements under the assumption of local thermodynamic equilibrium (LTE) in thermal plasma jets indicate about the deviation from LTE in thermal plasma jets. The electron number density measurement using Stark broadening of Ar-I (430 nm) line will be particularly useful when only argon gas is used in thermal plasma jets.
The European Physical Journal D 01/2003; 26(DOI: 10.1140/epjd/e2003-00211-9):215-219. · 1.48 Impact Factor
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ABSTRACT: The basic nature of arc root fluctuation in a plasma torch is an
extremely important factor from the point of view of improving and
optimizing performance of a plasma torch in present-day technology. In
spite of a number of ingenious attempts, this particular phenomenon is
still not fully explored. In this paper, voltage, acoustic, and optical
signals generated from a hollow cathode plasma torch are analyzed using
various tools of dynamical analysis such as real-time behavior, phase
portraits, power spectra, Lyapunov exponent, dimension, etc. Origin of
each of the signal in relation to arc-root fluctuation and mutual
correspondence among themselves are described in detail. For the first
time, all the signals are found to exhibit clear evidence of chaotic
behavior in all respect. A dimensional analysis reveals all the three
signals to be originated from the same chaotic phenomenon, i.e.,
fluctuation of are root
IEEE Transactions on Plasma Science 01/2001; · 1.17 Impact Factor
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ABSTRACT: Calorimetric measurements have been carried out in air to measure the heat flux delivered by an impinging plasma jet on a substrate placed perpendicular to the jet axis. The total heat flux delivered to the substrate has been resolved spatially using both Gaussian and exponential profiles with the profile constants determined from inversion of experimental data. It has been observed that the exponential profile gives a slightly better match with the experimental results compared to a Gaussian profile, which is more commonly used to represent concentrated energy flux beams such as plasma, electron or laser beams. Simultaneously, the conservation equations of mass, momentum and energy for the same plasma plume have been numerically solved to compute the stagnation heat flux profiles with conduction, convection, diffusion and radiation as the basic transport processes. An isothermal homogeneous, cylindrical, plasma column approximation has been applied in a modified form to take into account the energy lost due to radiation. The results from the simulation are compared with the experimental results. The degree of validity of the simplifying assumptions made in the analysis and their contribution to the discrepancy between the theory and the experiment are discussed.
Plasma Sources Science and Technology 03/2000; 9(2):108. · 2.52 Impact Factor
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ABSTRACT: In free burning as well as in stabilized arc columns, the inherent
movement of arc root results in fluctuation in arc voltage. A full
knowledge and control over the arc root dynamics can effectively
lengthen the life time, drastically improve performance and reliability
in arc plasma devices. In this paper, we experimentally investigate the
fluctuating voltage signals generated from an atmospheric pressure arc
discharge produced in a hollow electrode plasma torch. For the first
time, analysis of these signals reveal them to exhibit chaotic behavior.
The present analysis is supported with real time behavior, phase
portraits, power spectra and Lyapunov exponents. Dependence of system
behavior on various control parameters is also investigated. This
approach is interesting in the sense that it can lead to better
understanding of physics for future researches on arc plasma jets and
related devices
IEEE Transactions on Plasma Science 03/2000; · 1.17 Impact Factor
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ABSTRACT: The theory of dynamic similarity has been used to construct a generalized current-voltage characteristic (CVC) of a non-transferred, straight polarity, solid electrode arc-plasma torch. The enthalpy number obtained from the energy equation has been found to significantly influence the characteristics of the electric arc. The generalized CVC developed has been found to match with experimental parameters of other torches having the same basic principle of design and used elsewhere. The electrothermal efficiency of the plasma torch has been determined and put in the form of a generalized correlation using dimensionless numbers. The use of the theory of dynamic similarity to obtain a generalized correlation has been therefore found to be more appropriate.
Plasma Sources Science and Technology 12/1998; 8(1):100. · 2.52 Impact Factor
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ABSTRACT: The current-voltage characteristics and the electrode heat losses have been measured in a gas-stabilized DC arc generated in a non-transferred arc plasma torch operating on a mixture of argon and nitrogen. The applicability of a Nottingham-type relation between voltage and current to these arcs has been examined by correlating the measured electrode heat losses, plasma power and arc current under different flow rates and gas mixture ratios. The analysis has yielded the Nottingham coefficients which are used to estimate the arc voltage drop. The near constancy of the electrode heat loss per unit current has led to the implication that in stabilized arcs electrode heat loss is linear in current in the limit of small radiation/convection terms. In such cases the first Nottingham coefficient has been found to represent the electrode drop of potential. Secondly, in a nitrogen-argon mixed gas regime, when nitrogen flow rates are more than 20% of argon flow rates, one observes a saturation behaviour in the electrode drop of potential. Beyond this threshold, argon makes a negligible contribution to the arc electrical characteristics.
Plasma Sources Science and Technology 12/1998; 3(1):108. · 2.52 Impact Factor
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ABSTRACT: The excitation temperature of the plasma column in a spray torch can be determined using the atomic Boltzmann method. The spatially integrated intensities of emission lines resulting from Ar-I transitions in the wavelength region 400–451 nm have been measured. The central axis temperature of an inhomogeneous, axisymmetric, plasma column has been determined using a modified atomic Boltzmann technique without using the Abel inversion technique. The spectral measurements were made up to a distance of 20 mm from the nozzle exit point. The plasma torch was operated at power levels of 5 and 10 kW and the flow of argon was kept at 25 l/min. The average temperature of the plasma jet at the nozzle exit point was estimated using an energy balance technique. The temperatures estimated using heat loss data and the centre line temperature differ significantly. A simple analytical expression was used to relate the average temperature and centre line temperature at the nozzle exit point. The temperature profile parameter n has also been calculated.
Measurement Science and Technology 01/1997; 8(PH: S0957-0233(97)79472-4):1146-1150. · 1.49 Impact Factor
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ABSTRACT: Strontium ferrite films were deposited by RF sputtering of a
commercial strontium ferrite target onto fused quartz substrates
maintained at temperatures up to 900°C. Films deposited at
T <800°C were amorphous, but films deposited at
T >800°C had crystalline M -type strontium
ferrite structures. The thin composition corresponded to that of the
target. Films deposited at 800°C were partially oriented in the
[110] direction with the c -axis in the plane. Postannealing led
to an increase in the magnetization, indicating incomplete formation of
ferrite in the as-deposited state. Both in-plane and perpendicular
hysteresis loops are rectangular with remanence ratios of 0.8 and 0.6,
respectively, showing partial orientation with the c -axis. The
torque curve is consistent with the above, although there are some
additional anomalous peaks
IEEE Transactions on Magnetics 12/1993; · 1.36 Impact Factor
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ABSTRACT: We have prepared Fe/Ta multilayers by rf sputtering. A small 1-cm2 chip of Fe-57 was placed on the Fe target. We studied the magnetization (M) and M-H loops and also carried out conversion electron Mossbauer spectroscopy (CEMS). The in-plane loops are rectangular with a lowest coercivity of 2.6 Oe. Magnetization studies indicate a dead Fe layer about 5 angstrom thick at each interface. CEMS spectra for samples with t(Fe) greater-than-or-equal-to 54 angstrom showed a typical six-line pattern, indicating the presence of bulk Fe. No other Fe sites could be detected. However, for t(Fe) = 24 angstrom, where almost 50% of Fe is nonmagnetic, CEMS spectra showed the presence of a strong paramagnetic doublet.
Journal of Applied Physics 01/1993; 73(10, Part 2b):6438-6440. · 2.17 Impact Factor
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ABSTRACT: Magnetooptic (MO) polar Kerr effect spectra and MO hysteresis loops of SrFe12O19 hexagonal ferrite films are presented. The films were prepared by rf sputtering and subsequently annealed at 800 or 900°C in O2/Ar. The crystallographic orientation with the c-axis perpendicular to the film plane was checked using XRD. The films display perpendicular magnetic anisotropy and rectangular hysteresis loops with a remanence ratio close to one. At low photon energies below the absorption edge of SrFe12O19 at 2.5 eV MO spectra are affected by the radiation penetration into the film and the quartz substrate. Above this energy they display the features typical for bulk SrFe12O19 crystals. The coercive field, structure of the MO spectra and the magnitude of the prominent peak in the spectra near 4.5 eV can be correlated with the structural quality of the films. Consequently, the magnetooptics can serve as a diagnostics tool for these films.
http://dx.doi.org/10.1051/jp4:19971294.
